Energy generation is the main contributor to greenhouse gas emissions. For that reason, renewable energies, such as biomass, must play a fundamental role in climate change mitigation.

At the same time, improving waste management in order to achieve a completely circular economy remains another EU priority. The agri-food industries produce substantial volumes of waste, mainly organic, derived from the processing and packaging of products, and also from the cleaning of agri-food facilities. These wastes have to be treated, in most cases, at the location where they are produced or by an authorised waste manager. In some cases, the wastes enter the sewage system as a result of accidental leaks. These wastes commonly have a high water content, which increases their freight costs and makes their treatment difficult.

One alternative for treating this kind of waste is its co-digestion with wastewater treatment plant (WWTP) sludge, which neutralises the waste while producing biogas.

Spain has an available potential of 49.7 million tonnes/year of agri-food industry waste that could be used to generate 2 600 million m3/year of biogas, equivalent to 4.2% of Spain's annual natural gas production.

Objectives

The project will generate biogas by streamlining the co-digestion of agri-food industry waste and wastewater in a WWTP. The project will deploy in the WWTP an innovative waste dosage control technology applied in anaerobic digesters.

This new technology will also allow continuous measurement of the quantity and composition of the biogas that is generated, yielding better results through optimised digestion of both waste and sludge. Onsite energy production will also minimise freight costs.

The project will design and install two prototypes: one with the new dosage and measuring technology; and one with conventional technology. In this way the new technology can be compared to the conventional approach.

Expected results:

A 20% increase in biogas production through the most favourable waste and mixture dosage. Energy production at the WWTP is expected to be 115.59 megawatt hours/year, equivalent to an annual greenhouse gas emissions saving of 27.97 tonnes/CO2;

A minimum 8% increase in the content of methane in the biogas;

An increase of the capacity of waste co-digestion by 60%, resulting in further reductions in greenhouse gas emissions;

Greater stabilisation of the sludge, with reduced content of metals, meaning the sludge can be reused as an agricultural fertilizer; and

A 30-35% increase in the self-supply energy capacity of the WWTP, and optimisation of biogas production according to the energy demand of the plant, producing more biogas when demand is higher and less when demand is lower, thereby avoiding excess production that exceeds the storage capacity of the plant.